The invention relates to a crawler undercarriage mechanism, in particular for cranes, comprising an idler, a plurality of running rollers, a drive sprocket wheel and an endless chain of individual chain links releasably connected one to another. The sprocket wheel drive has running treads and wheel flanges at each side thereof. The chain links have guide webs, the guide web shaving bearing surfaces which interact with the running treads, and guide surfaces which interact with the wheel flanges. A guide web cam-like element interacts with chain teeth on the drive sprocket wheel.
A crawler undercarriage mechanism of the generic type is known from U.S. Pat. No. 4,176,887 (Alpers et al.). It has a single-piece drive sprocket wheel which is provided with cam-like chain teeth on the circumference and with a running tread on both sides. In each case one wheel flange is formed as a result of the difference in diameter between the larger diameter of the root circle of the chain teeth and the smaller external diameter of the running treads. An endless chain guided offer the drive sprocket wheel, an idler and a plurality of running rollers comprises individual chain links which are produced in one piece, are designed as double grouser track shoes and are connected releasably to one another by means of bolts and interengaging outer and inner link plates. Each chain link has two guide webs which are located symmetrically in relation to the center and are spaced apart from one another in the running direction. On the top side, they are provided with a rectilinear bearing surface, which interacts with the running treads,land, on the inside, they are provided with a guide surface, which interacts with the respective wheel flange of the drive sprocket wheel. Arranged between the two guide webs is a cam which connects the two webs and interacts with the chain teeth. The cam is provided, on both sides, with rectilinear engagement surfaces which terminate in a cutting edge. At the transition from the planar engagement surfaces to the base plate of the chain link, the two-sided cam has a recess on both sides.
The object of the invention is further to develop a crawler undercarriage mechanism of the generic type in order, by reducing the surface pressure, to minimize the wear and to improve the guidance of the endless chain, with the high transmission capacity not being reduced in any way.
In accordance with the invention, the drive sprocket wheel has an involute toothing arrangement which meshes with a rectilinear flank of the cam-like element. By virtue of this toothing-arrangement geometry, the drive sprocket wheel/chain link pairing is approximately equivalent to a gearwheel/rack system with the advantages listed hereinbelow.
The surface pressure between the drive sprocket wheel and endless chain can be changed by the involute line being varied.
At the run-off point of the endless chain, the location of contact between the drive sprocket wheel and cam-like element of the endless chain is displaced outward along the involute, i.e. the wear is distributed over a relatively large region.
Force is transmitted in the region of the center of the involute tooth flank, i.e. the tip of the force-fitting tooth of the drive sprocket wheel is not subjected to loading.
An involute toothing arrangement is not affected by the change in the axial spacing of the meshing chain links. It is thus the case in the present system that the kinematics are not affected in any way by the endless chain moving up the drive sprocket wheel on account of chain lengthening or the penetration of dirt.
According to a further feature, the top side of the respective guide web has a concavely curved bearing surface, which interacts with the convexly curved running-tread surface of the drive sprocket wheel. The internal diameter of the concavely curved bearing surface is preferably equal to the external diameter of the convexly curved running-tread surface. In other words, the radius of curvature of the guide web concavely curved bearing surface corresponds to one-half the external diameter of the running tread surface. This configuration ensures a defined position in relation to the drive sprocket wheel, with the result that tilting cannot occur. Moreover, in a known manner, the two inner surfaces of the guide web perform the function of guiding the drive sprocket wheel and the two outer surfaces perform the function of lateral guidance between the running rollers.
It, is also advantageous that the shape of the chain tooth and the increase in the size of the opening of the endless chain as it runs onto the drive sprocket wheel aid the discharge of dirt.
According to a further feature, the drive sprocket wheel is designed in a number of parts with a centrally located toothed wheel rim and two running treads fastened releasably thereto. This arrangement makes it possible for the toothed wheel rim to be produced from a more wear-resistant material than the running treads; This achieves a longer service life of the drive sprocket wheel in relation to dirt and abrasion between the endless chain and drive sprocket wheel.
In order for it to be possible, with the selected configuration of the chain link, for large forces to continue to be transmitted, six outer link plates are arranged on one longitudinal side and four inner link plates, offset in relation to the outer link plates, are arranged on the opposite side. When two chain links are attached to one another, in each case three outer link plates and two inner link plates are connected by in each case one chain bolt, this producing a double-shear connection by means of which high forces can be transmitted. The chain bolt is secured against slipping axially by means of a screw/nut connection which is arranged in each case on the outside of the first and third outer link plates.